Lounge details for KUL can be found in the
BA Lounge Database | Far East
Malaysia Airlines have lounges in both the main terminal and the satellite which are all detailed in the wiki. Personally speaking, I found the Malaysia First Lounge in the satellite to be a very nice spot to pass some time. It has an a la carte dining room as well as sleeping pods. It was also very quiet during the late evening while waiting for the BA34 to LHR.